1. Field of the Invention
This invention relates to a window assembly for use in a space environment to support an inflatable human habitat module or other inflatable space structure.
2. Description of the Prior Art
Windows have been an integral part of manned spacecraft since the inception of space flight. A window serves many purposes such as allowing the inhabitants of a spacecraft to avoid a closed-in or claustrophobic feeling and assisting extra-vehicular activities by observing events outside the craft.
The usual application of a window has traditionally been in conjunction with a solid, or hard, shelled space vehicle. In this use, a window frame is attached to a rigid structural wall of a craft. This is roughly similar to the use of a window in a conventional aircraft. There are, however, major differences between a rigid hulled space vehicle and an inflatable module.
A typical inflatable module has an air barrier, a restraint layer, and an orbital debris shield. Each layer is designed to address a particular issue that is encountered in a space environment. The debris shield affords a level of protection against hypervelocity impactors penetrating the hull and causing a loss of the module's air into space. The air bladder provides the primary impervious barrier to prevent gas flow and the restraint layer provides structural support against the loads induced by the pressure.
Modules having these basic characteristics are identified in U.S. Pat. No. 6,231,010 to Schneider, et al and U.S. Pat. No. 6,547,189 to Raboin, et al. Each of these patents briefly alludes to, but does not claim or provide a detailed structure for, a window as part of an inflatable module.
One of the key advantages to an inflatable module is that the module can be folded into a confined space prior to launch, thereby making it easier to fit within a launch vehicle payload, and then inflated to a significantly larger volume upon deployment into space.
Consequently, each of the layers of an inflatable module must be flexible to allow for folding and unfolding of the shell. As each layer serves a different function, the characteristics and materials in each layer will be different. This requires the window assembly to accommodate each layer in a different way. For example, the window assembly would be seal bonded in an airtight fashion to the air barrier and provide attachment points for the straps in the restraint layer in a different fashion.
This is an atypical approach that is distinct from the type of window assembly that would be used in a solid shelled space vehicle. In a rigid hulled structure, the window assembly would not move in relation to the hull. Furthermore, an inflexible hull would usually not have a plurality of layers where each layer would require a different attachment means.
In the case of an inflatable module, the window assembly, while not flexible, must not damage the flexible shell when the shell is folded or unfolded. Also, the assembly must interact with the layers of the hull to provide a sufficient airtight integrity to substantially sustain the atmosphere within the module when the spacecraft is deployed.
Another aspect of a window assembly is that it must not become opaque due to fogging. This is where the water in the air condenses on the surface of the window due to a difference in temperature across the viewable window surface between the internal module environment and that of space. To lessen this problem, the window assembly has a channel between viewable layers to equalize pressure and reduce fogging.